Previous treatments of nitrile rubbers and similar copolymers with strong acids resulted in deleterious alteration of the rubber. Current work indicates that azine, amide, sulfonic acid, sulfates, hydroxyl and cyclization form from treatment of nitrile rubber with concentrated sulfuric acid. After such treatment the rubber surface becomes hard and stressed, a layer beneath the hardened surface is weakened and subsequent reaction with an epoxy results in some covalent bonds which are prone to hydrolysis or destruction by other reactions. Moreover, the unsaturation concentration decreases. The rubber thus losing its rubbery property becomes useless and in fact dangerous to employ particularly, in modern military systems, as well as, commercially.
Although no literature on the subject of nitrile rubber surface hydrolysis was observed, references concerning nitrile and amide hydrolysis appear to span about forty years. What is revealed is that nitrile hydrolysis requires rigorous conditions of heat and strong base or acid. Rabinovitch et al., Canadian Journal of Research, 20-secB 121 1942 studied the hydrolysis of propionitrile in aqueous hydrochloric acid solutions. In acid concentrations above 4N they found that the overall rate of hydrolysis was dependent upon the decomposition of intermediate amide and below acid concentrations of 4N, the nitrile decomposition was rate determining. Increasing the acid concentration from 5N to 6.48N resulted in an hydrolysis rate constant increase from 0.0174 hr.sup.-1 to about 0.1 hr.sup.-1. M. L. Kilpatrick, J. Am. Chem. Soc., 69 40 1947 showed that the rate of hydrolysis of cyanamide was the same in dilute solutions of various strong acids. In HCL, it was found that the rates rose with acid concentration but then dropped off at a relatively low acid concentration. Sperber et al., Journal of American Chemical Society 70, 3091 1948 shows the hydrolysis of tributyl acetonitrile in strong sulfuric acid delivers high yields of amide. The same authors were unable to hydrolyze tributyl acetamide at elevated temperatures in phosphoric, concentrated hydrochloric, or sulfuric-acetic acid mixture. They concluded sterically hindered amides are very difficult to hydrolyze. Tsai et al., Journal of the American Chemical Society, 79, 2530 1957 in studying steric effects in the hydrolysis of hindered amides and nitriles came to the same conclusion as Sperber et al.